Multicavity klystron for microwave and uhf with interfering mode suppression slots in the ends of the drift tube



Apnl 28, 1970 E. DEMMEL 3,509,412

MULTICAVITY KLYSTRON FOR MICROWAVE AND UHF WITH INTERFERING MODE SUPPRESSION SLOTS IN THE ENDS OF THE DRIFT TUBE Filed Dec. 20. 1967 FIG] INVENTOR. HVZIO DEMMEL BY w. a A

41,09 Int. Cl. H01j 25/10, 23/20 US. Cl. 315-5.39 5 Claims ABSTRACT OF THE DISCLOSURE A multicavity klystron for microwave and UHF with a drift tube which connects the cavities. The ends of the drift tube are provided with slots extending from the outer wall to the inner wall and which extend in an axial direction for suppressing interference modes. These slots may have positions which are shifted 90 relative to slots in the other end of the same portion of the drift tube.

This invention relates to a multicavity klystron for the microwave and UHF-regions having a centrally-arranged multicavity through which an electron ray passes and which is interrupted in the chambers for acting on the electron ray, an airgap being present between its two ends terminating in each chamber.

Multicavity klystrons for the frequency ranges above identified are known in a great variety of forms. It is also known that these klystron devices can operate not only on a given frequency, the so-called fundamental mode, but under certain conditions also oscillate at several other frequencies, so that the desired operation is liable to be considerably disturbed. With such a multicavity klystron placed in a pulse-modulated amplifying device it was found that the output signal of the klystron was materially distorted and partly collapsed in a certain region of the ray voltage. The distortion of the output signal in a given region of the ray voltage was found to be caused by the occurrence of a self-generated oscillation of, for example, 8000 mc./sec., whereas the klystron was operated at a frequency of approximately 3000 mc./sec. The occurrence of this self-generated oscillation premises that at least two of the cavities of the tube design have the same mode of oscillation at neighbouring frequencies and that sufficient feedback also exists between the relevant cavities, which may be given, for example, by the H -mode in the drift tube connecting the cavities.

It is known to suppress such oscillations. by detuning one or a plurality of the relevant cavities, for example, by displacing a diaphragm or by means of a short circuit piston connected through a high-frequency coupling. However, such steps also influence the mode desired so that they are only of insignificant value.

The present invention avoids these disadvantages and is based on recognition of the fact that selective influencing of the interfering modes is possible since, in contrast with the cavity modes usually employed in klystrons, the interfering modes exhibit an azimuthal dependence upon the magnitudes determining the field and the wall current. To suppress self-generated interference oscillations in such characteristic modes, the invention therefore suggests forming at least one slot of suitable length in at least one end of the drift tube in at least one cavity, which slot begins at the airgap and extends in the axial direction.

Due to these steps, the interference modes are inductively loaded and shifted to lower frequencies to an extent United States Patent 0 dependent upon the dimensions of the slot formed, so that self-oscillation no longer occurs as a result of the frequency difference thus obtained between the modes taking part in the self-generating oscillation. Furthermore it appeared that the interference modes are not only shifted to lower frequencies but also their amplitude is attenuated. Due to the steps according to the invention, the mode used in the klystron is influenced netiher in frequency nor in coupling properties to any appreciable extent.

In a further embodiment of the invention at least one end of the hollow guide may be provided with a plurality of slots of equal or different lengths having positions which are mutually shifted by Also, one end of a portion of the hollow guide may be provided with slots which are shifted by 90 relative to slots formed in the other end of the same portion of the hollow guide. According to the invention it is also possible for both ends of the hollow guide located in a cavity to be provided with slots situated in 90 shifted positions. In all these devices the width of the slot may be small relative to the transverse dimensions of the hollow guide.

If two modes spatially shifted by 90 with respect to each other occur at neighbouring frequencies, it is possible to ascertain self-generated oscillations of adjacent frequencies. To suppress the two modes of oscillation it is then necessary to form either two slots, or two pairs of slots which are shifted 90 in position. This arrangement may be realized in the manner above described. It is then necessary only to consider that equally oriented modes exhibit a considerable frequency difference in different resonators.

The invention wil now be described with reference to the accompanying diagrammatic drawing, in which:

FIGURE 1 shows a multi-cavity klystron;

FIGURES 2a and 2b are plan views on the tube ends of the drift tube.

FIGURE 1 shows a centrally-arranged drift tube 1 through which an electron ray passes. The drift tube 1 is interrupted in cavities 2 in order that the electron ray may be influenced by an electric high-frequency field active in a gap 3. The two ends 4 and 5 of the drift tube lie in the cavity 2 and form therewith an assembly which is capable of resonating. The drift tube 1 forms the connection to the next cavity 2, which connection is indicated by a broken line 6 since, for example, another cavity 2 may be arranged at this area. The invention is not confined to the rotation-symmetrical embodiment of the drift tube and cavities which is shown and can use a different cross-section.

The incoupling and outcoupling devices in the cavities 2 are omitted for the sake of clarity. Such a system of double cavities may be caused to resonate upon occurrence of an interference mode at a given value of the ray voltage. An interference oscillation may be prevented by forming axial slots 7 in the ends 4 and 5 of the hollow guide 1, which constitute an inductive load for the interference mode and may be regarded as short circuited branch guides for the interference mode.

The slots 7 in the upper cavity may be formed in position shifted 90. Also, the slot 7 in the guide portion 8 in the upper cavity may have a 90 shifted position relative to the slot 9 in the lower chamber. In this example it has been assumed that the guide portion 8 also extends into the lower system and another cavity is not interposed.

FIGURE 2 is a plan view on the lower ends 4 and 5 of the drift tube 1, each having two slots 7 situated at right angles to each other, thus suppressing the two interference modes in one cavity.

The drift tube 1 need not extend into the cavity 2 at its two ends 4 and 5. It is also possible that, for example, the

outer edge of the end 4 lies in the inner surface of the wall 10 of the cavity 2. In this case the interference modes must be suppressed at the remaining end 5 in the cavity by forming corresponding slots 7 and 9 respectively.

According to the invention the width of the slots must be small relative to the transverse dimensions of the drift tube 1, that is to say in the rotation-symmetrical design of the drift tube 1 the width of the slots must be small relative to the diameter of the drift tube 1, in order that the fundamental mode or the desired mode is influenced to the least possible extent.

I claim:

1. A klystron for the microwave and UHF regions comprising a plurality of resonant cavities, a drift tube connecting said resonant cavities and terminating in each cavity resonator and defining an interaction gap therein, at least one interference mode suppressing slot extending from the inner to the outer surface and of suitable length in at least one end of the drift tube in at least one cavity resonator, said slot beginning at the airgap and extending in the axial direction.

2. A klystron as claimed in claim 1, wherein at least one end of the drift tube is provided with a plurality of slots having positions which are mutually shifted by 3. A klystron as claimed in claim 1, wherein one end of a portion of the drift tube is provided with slots which are shifted by 90 relative to slots in the other end of the same portion of the drift tube.

4. A klystron as claimed in claim 1, wherein both ends of the drift tube located in a cavity are provided with slots situated in positions shifted 90.

5. A klystron as claimed in claim 2, wherein the width of the slots is small relative to the transverse dimensions of the drift tube.

References Cited UNITED STATES PATENTS 2,939,037 5/1960 Jepsen 315-5.52 3,287,673 11/ 1966 Hammersand 3 15-5 .52 3,376,524 4/1968 Wang 315--5.39 X

HERMAN KARL SAALBACH, Primary Examiner S. CHATMON, JR., Assistant Examiner US. Cl. X.R. 315-552; 333-83 @23 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3509412 Dated April 28, 1970 Inventor(s) ENZIO DEMMEL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 27, change "multicavity" to read --drift tube-;

Column 2, line 62, change"90 shifted position" to read --position shifted 90;

line 63, change "chamber" to read --cavity;

Signed and sealed this 4th day of August 1970.

Aneat:

mm 1:. sum. .18. Austin; Officer Oonmiaalom at Patna 

